Lamda sensors

[darrenp]

Hi all
Does anybody have any usfull info on these little gits, I ave just had my first MOT on my VTS Xsara (2.0 16v) and it passed ok but was told that the lamda sensor maybe getting a bit iffy as the way the emissions reacted to on/off throttle action (been told this is common and indicates lamda failure).
From what I can gather on the net the sensors will have either one, two or four wires depending on how the heating element in them works, ok no problem but Citroen want £90 trade for one that fits a VTS so i phoned Andyspares and was told that they dont do one for the VTS. Will one of the universal ones work (I will ofcouse check the wires)as from what i seem to understand is that they all give the same voltage readings for a specific percentages of oxygen content in the exhaust gas, This also leads me to believe that it shouldnt matter what size engine i have as the sensor doesnt measure the volume of gas passing it just the ratio of oxygen found in the sample it comes into contact with.
I hope I havent confused anyone here as I almost got lost in that little lot but i need help, I begrudge paying £90 to Citroen for a sensor that is the same as a £35 jobbie just with a plug and a pretty citroen bag.
Can anyone help Please
Many thanks
darren.....